1. Field of the Invention
The present invention relates to a method for grinding the seal edge of a glass funnel and an apparatus therefor, in particular grinding method and apparatus for grinding the seal edge of a glass funnel for a cathode-ray tube.
2. Discussion of Background
Glass funnels, which form a cathode-ray tube for a TV set, a display and other devices, have a seal edge thereof ground by a grinding apparatus before having been assembled into the Cathode-ray tube since the seal edge is required to have proper surface roughness and good flatness.
An example of such a grinding apparatus, there is the grinding apparatus disclosed in JP-A-1034505, wherein a glass funnel is rotated with the seal edge thereof directed downward, and rotating grinding wheels are pressed against the seal edge to grind the seal edge. This grinding apparatus presses the grinding wheels against the seal edge by a weight to grind the seal edge at a constant pressure in order to improve the grinding precision of the seal edge.
On the other hand, the grinding apparatus disclosed in JP-B-533114 presses the seal edge of the glass funnel against grinding wheels by a weight to grind the seal edge at a constant pressure. This grinding apparatus includes a device for stopping the downward movement of the glass funnel when the glass funnel has lowered to a location corresponding to a set grinding removal.
However, the grinding apparatuses disclosed in JP-A-1034505 and JP-B-0533114 have created a problem in that it is impossible to improve grinding efficiency since the apparatuses grind the seal edge at a constant pressure all the time.
This problem may be eliminated by making the weight load heavier to increase the level of the constant pressure. However, if the pressure is increased too much, the flatness of a ground surface has been deteriorated because of variations in the behavior of the grinding wheels, and a defect, such as a chip, has been caused at the seal edge in some cases.